Transducers convert signals from one domain to another and are often used in sensors. A common transducer used as a sensor that is seen in everyday life is a microphone, which is essentially an audio signal transducer that converts sound waves to electrical signals.
One way of constructing a microphone is by using a microelectromechanical system (MEMS) based sensor that gathers information from the environment by measuring a change in an electrical parameter in response to a mechanical movement. For example, MEMS microphone may have a movable diaphragm having a capacitance that varies with physical deflection. Electronics attached to the MEMS then process the signal information derived from the sensors. MEMS devices may be manufactured using micromachining fabrication techniques similar to those used for integrated circuits.
Audio microphones are commonly used in a variety of consumer applications such as cellular telephones, digital audio recorders, personal computers and teleconferencing systems. In a MEMS microphone, a pressure sensitive diaphragm is disposed directly onto an integrated circuit. As such, the microphone is contained on a single integrated circuit rather than being fabricated from individual discrete parts.
MEMS devices may be formed as oscillators, resonators, accelerometers, gyroscopes, pressure sensors, microphones, microspeakers, micro-mirrors, and other devices, and often use capacitive sensing techniques for measuring the physical phenomenon being measured. In such applications, the capacitance change of the capacitive sensor is converted into a usable voltage or current using interface circuits. In order to operate such capacitive sensors, the interface circuits may include biasing elements, such as a charge pump and sensing elements, such as resistors, capacitors, and amplifiers. The design and manufacture of the interface circuit introduces numerous characteristics to the capacitive sensor behavior.